Along with recent advancement toward higher integration and lager capacity of large scale integrated circuits (LSIs), the circuit line width to be required for semiconductor devices has become smaller and smaller. The photolithography technique is used to form desired circuit patterns in semiconductor devices. In this photolithography technique, pattern transfer is performed using a defined pattern called a photomask or a reticle. A charged particle beam drawing apparatus having fine resolution is used to produce highly accurate masks to be used for such pattern transfer.
As an example of the charged particle beam drawing apparatus of this type, there has been developed a charged particle beam drawing apparatus configured to draw a pattern on a specimen, such as a mask or a blank, on a stage by deflecting and focusing a charged particle beam onto a predetermined position on the specimen on the stage while moving the stage on which the specimen is placed. In the charged particle beam drawing apparatus, an optical lens barrel is placed above a drawing chamber that constitutes a specimen space. The optical lens barrel incorporates a charged particle optical system for projecting the charged particle beam.
In the charged particle beam drawing apparatus described above, the drawing chamber functioning as a vacuum container slightly changes its shape due to an influence of the atmospheric pressure when the drawing chamber is set to a vacuum state by decompression. In this case, drawing accuracy may deteriorate if the stage inside the drawing chamber is tilted by a deformation of a bottom surface, i.e., a bottom plate of the drawing chamber and the projection position of the charged particle beam deviates from the predetermined position. For this reason, the drawing chamber is formed to have sufficient rigidity so as not to cause a significant deformation even when the inside of the drawing chamber is set to the vacuum state.
However, in order to impart the sufficient rigidity to the drawing chamber, a thickness (a plate thickness) of the bottom plate has to be increased, for example, which makes the drawing chamber very heavy. Particularly, the drawing accuracy recently required is accuracy with an allowable range of several micrometers, and a deformation of the drawing chamber by about tens to hundreds of micrometers even causes a problem. In this regard, the bottom plate needs to be made thicker and the weight of the drawing chamber tends to be increased accordingly.